Credit for the included axial jet drive calculation spreadsheet, goes to RCgroups member UnusualRC. UPDATE: I've been notified there is a mistake in one of the formulas on the sheet. Please be aware of that.

TODO:

Get video of it at top speed with CoG moved foward running at 6S then retest

DONE:

Test boat with 6S configuration. boat is way overpowered which is great fun. SO fast. Gets a lot of air.

IN PROGRESS

Make next version with bigger hull - calculations were incorrect and hull sat far deeper in the water than calculations indicated

Improve lid to be more water tight on next version.

Other side notes:

batteries, esc and motor all stayed stone cold in 3S mode running at full speed. Motor is wayyy oversized for this boat.

It nowhere near uses the full power available to it running at 3S.

Materials and methods

I printed my hull at 0.3mm layers with 3 perimeters and 25% infill with support structures enabled. The hull is best printed in PETG or ABS for durability. I've printed my impeller in PLA because of how it is easier to get a very clean print when using support material. I find it prints best at 0.15mm so highly recommend that.

The impeller is intended to be glued onto your 3mm drive shaft. Its recommended that you sand the shaft lightly before gluing to ensure a good bond.

The nozzle takes a 3mm inner, 4mm outer diameter teflon tube as a bushing for the shaft (check the last two pictures above). I cut 5mm off my bowden tube and used this. Teflon is a very durable and low friction material - perfect for use here.

Bill of Materials:
- ~430g of filament
- M3 misc screws
- self tapping screws
- 1x 100mm long, 3mm stainless steel rod as driveshaft.
- 1x 623RS bearing (623ZZ is also fine but rubber seal is of course better when water is involved)
- 1x 750mm of servo pushrod wire
- 1x flexible coupler to go from motor to the driveshaft. I used 3 to 5mm adapter. Most 36mm diameter motors use 5mm shafts. I would recommend a universal joint which can be found for $1-2 on aliexpress. You could print your own universal joint or direct coupler (both are printable and included in files).

- 1x Motor + ESC
I'll be using this motor: https://hobbyking.com/en_us/turnigy-xk3674-1900kv-brushless-inrunner.html
And this ESC: https://hobbyking.com/en_us/hobbyking-120a-boat-esc-4a-ubec.html

You'll want to pick a motor/battery combo that delivers up to 20,000 rpm and can handle about ~75A continuous. Refer to: https://www.kehrer-modellbau.de/en/kmb-jet28/jet-drives/kmb-jet28-rev.-3-with-short-steering-nozzle

Included in the files are mounting brackets for 36mm and 28mm diameter inrunner motors as well as a mount for common airplane motors using 19mm hole spacing. If you need a bracket for a different motor, let me know the dimensions and I'll make one up for you.

- 2x lipo batteries. You'll want two: one to place in either side of the motor for balance. I will use 2x 2200mAh 3S lipo batteries. I like to use velcro to hold batteries in place.
- 1x transmitter/receiver set. I will be using my Flysky i6 transmitter with receiver

If you have any questions, please do ask. As noted at the top of the page with a link, there is now an improved new version published.

Thanks! Yes I've just uploaded the STL file for the lid. It doesn't seal very well but it should be ok if you use a soft foam strip. The next version of the design will have a much better lid since this the surface is flat. It is much easier to design a lid for it: https://i.imgur.com/QHB7cP0.png

I haven't made much progress on it lately since university has been really busy and other things have been soaking up a lot of time. If you ever want any other files just let me know and I'll upload them :-)